There are a great number of different versions of magnet units, particularly for thermoelectric flame failure devices on gas-fired appliances. Their function is to switch off the flow of gas to a burner as soon as the gas flame on the burner is extinguished for any reason. What happens essentially in such a case is that a thermoelement forming part of the flame failure device ceases to be heated. This cuts off the electricity supply to a solenoid forming part of the magnet unit and causes a gas valve to be closed.
The published patent application DE 12 17 896 A describes a magnet unit for a thermoelectric flame failure device consisting of an anchor plate connected to a valve plunger and a solenoid with a coil that is held on a supporting plate. On the outer side of the supporting plate there is an electrical contact head connected to one end of the field coil which is electrically insulated from the supporting plate and around whose peripheral area a protective cap is attached enclosing the anchor plate and the magnet. The other end of the field coil is attached between the protective cap and the peripheral area of the supporting plate.
A version of a safety gas valve with electromagnetic coupling is known from utility model patent application DE 200 04 755 U1. This has basically a similar structure to the magnet unit already described above. Here too one end of the coil wire inside the supporting plate, termed the base in this case, is led to a contact which is also electrically insulated from the base. The other end of the coil wire is connected to an additional ground wire which is electrically welded on the periphery of an annular bulb on the base.
In both these versions it is disadvantageous if one end of the coil gets pressed between the protective cap and the peripheral area of the supporting plate. This causes the protective cap to fail to sit evenly and become distorted at that point. Apart from the resulting gap through which dirt can penetrate into the area enclosed by the protective cap, thus impairing the function of the magnet unit, the tightness of fit of the protective cap is weakened.
In another version of a magnet unit, as described in DE 19 59 057 A, a patent application open to public inspection, the coil of the solenoid is positioned on a coil former fitted with two feet with which the coil former is pushed onto two power lead pins which are electrically insulated and extend through the supporting plate into the inside of the magnet unit. The ends of the coil are united in slots in the power lead pins and soldered.
While an even sit of the protective cap is achieved with this magnet unit, the solution is very costly and thus not very suitable for series production.
With other known magnet units, as described, for example, in the German patent specifications DE 22 14 063 C3 or DE 23 54 014 C3, one end of the coil is electrically conductively connected with a soldered connection of a soldering bulb which is electrically insulated and extends through the supporting plate. The other end of the coil is soldered on the upper side of the supporting plate.
Apart from the comparatively complicated structure, it is difficult, especially when taking into account the actual proportions, to position the soldering joint on the upper side of the supporting plate and to carry out the soldering without weakening the firmness of the sit of the plastic cap on the supporting plate. Whilst subsequent rework is conceivable, it is not an ideal solution because of the expense involved, especially in series production.